Available online at www.sciencedirect.com ScienceDirect Procedia Computer Science 79 (2016 ) 785 792 7th International Conference on Communication, Computing and Virtualization 2016 Electromagnetic Energy Harvester for Low Frequency Vibrations using MEMS Prof. Ankita Kumar0F*, Prof.S.S.Balpande, Prof. S.C. Anjankar Assistant Professor in Electronics Engineering Department, Ramdeobaba College of Engineering and Management- an Autonomous institute affiliated to RTMNU, Nagpur, India Abstract This paper proposes design and analysis of electromagnetic energy harvester using MEMS technology. The energy harvester is intended to harvest energy from low frequency ambient vibrations that is less than 100Hz. The design would consist of a cantilever which is the simplest MEMS structure which can further be used to power the amplifiers. These amplifiers can be used to amplify the low amplitude and low frequency vibration signals. The work intends to explore the opportunities in harnessing vibrations induced by the live loads, such as laden Lorries & Buses on bridges, to harvest energy in the form of generated voltage. A cantilever based electromagnetic energy harvester can be employed to capture these miniscule level of vibrations and convert them into electrical energy. The Faraday's law of electromagnetic induction is the fundament idea utilized to design the cantilever beam simulated with dimensions of 2500x500μm. The material plays a vital role in sensitivity and hence NdFeB is selected as magnetic material whereas Aluminum as the conducting coil electrode material. The voltage of 2.34 mv is generated using single cantilever beam energy harvester. An array of six such cantilevers generates a voltage of 3.27 mv. The simulation results confirm that the low ambient vibrations can be effectively utilized to generate useful energy. 2016 The The Authors. Authors. Published Published by by Elsevier Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of ICCCV 2016. Peer-review under responsibility of the Organizing Committee of ICCCV 2016 Keywords:MEMS; Electromagnetic; Energy Harvester; Low Frequency; Cantilever Beam. 1. Introduction Vibrations are a severe issue of discussion and control of mechanical structures as it may generate noise, reduce stability, and introduce cracks in structure. Innovations for controlling and suppressing such unwanted vibrations are being carried out by many researchers. However, the main problem is monitoring the real time vibrations. The * Ankita Kumar is the Corresponding author. Tel.: +91-9850-359-338 +91-9850-395-340; fax: +91-712-2583237 E-mail address: ankitakumar1187@gmail.com, kumaraa6@rknec.edu 1877-0509 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of ICCCV 2016 doi:10.1016/j.procs.2016.03.104
786 Ankita Kumar et al. / Procedia Computer Science 79 ( 2016 ) 785 792 vibrations caused by loads and environmental conditions on mechanical structures like bridges are in the normally in the range of 100-200 Hz [1]. If these vibrations are engineered properly to channelize this waste energy into useful energy then a lot of problems regarding powering of monitoring and display devices for these structures can be solved. Hence, the electromagnetic energy harvester has been designed to convert such vibrations in the range of 100-200 Hz of frequency range into useful electrical energy. This frequency range is the multiple of actual vibrations that occur in bridges [2]. The generalized block diagram showing the energy harvester system where is shown in Fig.1. Fig.1 Block Diagram of Energy Harvester System 2. Principle behind the electromagnetic energy harvester The basic principle in the design of electromagnetic energy harvester is Faraday's law of electromagnetic induction show in Fig.2, which states that whenever a conductor moves inside a magnetic field, there will be an induced current in it. Thus, based on this principle a basic initial design was modeled shown in Fig.3. Fig.2 Interaction of Magnetic fields and current carrying conductor Fig.3 Basic Design of Energy Harvester (Side View) based on Faraday s Law of Electromagnetic Induction [4] Fig.3 shows a cantilever beam with a conducting material i.e. an Aluminium coil on the tip mass. When the vibrations cause the cantilever beam to deflect in Z direction, the Aluminium coil cuts the magnetic field of the magnetic material (NdFeB) placed at a distance of 100 μm from the cantilever beam, in effect generating some voltage across the Aluminum coil [3]. 3. Vibration modes and Resonance A cantilever beam essentially has multiple modes of vibration, with each mode having a different resonant frequency. The first mode of vibration has the lowest resonant frequency and typically provides the most deflection and therefore electrical energy. More power is produced at lower frequencies and is hence desirable for the cantilever design [5]. The characteristic mode curves of each mode defines the deflection of the beam along its length. Figure 4 reflects upon some examples of mode curves for the first three vibration modes of a beam. The deflection will vary in
Ankita Kumar et al. / Procedia Computer Science 79 ( 2016 ) 785 792 787 sinusoidal manner when the beam is deflected. The points where the mode shape is zero are stationary and are referred to as nodes. In general, the n th vibration mode will have n nodes. Considering this concept, the cantilever beam is designed to be rectangular in shape so that frequency of operation (100Hz to 200Hz) is targeted in 1st and 2nd mode for maximizing harvested power. Fig 4 Deflection of Beam for 1st three resonant Modes [6] 4. Energy Harvester Design From Fig.1, it can be seen that to process the signals an instrumentation amplifier is needed. This instrumentation amplifier needs to be driven by external batteries. The Precision Low Power Instrumentation Amplifiers such as INA12xP series require minimum of 4.5 V to operate. Hence, if we are able to produce 4.5V using the ambient vibrations we would not need external batteries to run the system. In order to maximize the harvested energy we will be using electromagnetic induction effect. Also, for stronger magnetic field, it is necessary that the maximum area of the coil should cut the magnetic line produced by NdFeB magnet. Hence a square shaped coil structure was deposited on the cantilever beam. The top view of the design is shown in Fig.5. Fig.5 Top View of Electromagnetic Energy Harvester 4.1. Simulation of Energy Harvester in COMSOL Multiphysics Initially, an analysis to determine the displacement with respect to frequency has been carried out to verify whether the selected dimensions for the cantilever beam will provide sufficient displacement due to vibrations. This is shown in Fig. 6. After verifying the sufficient displacements i.e. around 7 millimeters for frequency of 34 Hz it has been verified that the materials used provide sufficient displacement due to vibrations to generate voltage. Now, array of 3 cantilevers have been designed without electromagnetic effect which yielded 1.05mV as shown in Fig 7a.
788 Ankita Kumar et al. / Procedia Computer Science 79 ( 2016 ) 785 792 a. Fig 7a. Normal Cantilever Design b. Fig 7b. Modified Electro-Magnetic Cantilever Design Fig.6 Frequency vs Displacement for Electromagnetic Energy Harvester Fig 8 shows the array of cantilevers for the modified design of energy harvester based on electromagnetic effect. It can be seen that the array of 6 cantilevers is yielding a voltage of 3.2658 mv which is much larger than the array of normal cantilever beams which yielded 1.05 mv. Fig.8 Array of Modified Energy Harvester Hence, 32.41% increase in generated voltage is obtained with modified electromagnetic induction based cantilever design at 100 Hz frequency. Resultantly, when this generated voltage is fed to a voltage multiplier unit i.e. the processing circuit in the block diagram it can yield a voltage of 4V to drive the instrumentation amplifiers as shown in Fig 1. Fig.9 Power vs Frequency for an array of six cantilevers
Ankita Kumar et al. / Procedia Computer Science 79 ( 2016 ) 785 792 789 However, the frequency could not be reduced below 100 Hz. This is due to the constraint that further decrease in the frequency requires the length of the cantilever beam needs to be increased. Therefore, a tradeoff in frequency and dimensions has been decided as 100 Hz. The power generated [5] by these cantilever beams [7] is of at most importance. The power generated by an array of 6 Electromagnetic cantilever beams for low frequencies to drive the precision low power instrumentation amplifiers is plotted in Fig.9 4.2. Electromagnetic Energy Harvester Dimensions The Electromagnetic Energy Harvester Design dimensions are mentioned in Table I. These dimensions are justified by virtue of the simulation results from Fig. 7a showing that the normal cantilever beam which is not under any magnetic effect does not generate sufficient power as compared to that designed under the effect of magnetic field Fig 7b. Table II describes the material properties of the cantilever beam. Table I: Energy Harvester Dimensions Material Length Width Thickness Silicon Substrate 2500 μm 500 μm 50 μm Silicon Anchor 500 μm 500 μm 150 μm Silicon Cantilever Plate 2500 μm 500 μm 10 μm Silicon Proof Mass 500 μm 500 μm 20 μm Aluminum Deposition 400 μm 100 μm 5 μm NdFeB Deposition 100 μm 500 μm 5 μm Table II: Material Properties of the Energy Harvester Design Material Density Young s Modulus Poisson s Ratio Silicon 2.329g/cm3 130-188 GPa 0.064-0.28 Aluminium 2.7 g/cm3 70 GPa 0.35 NdFeB 7.5 g/cm3 100 GPa 0.24 5. Macro Level Prototype of the Design To verify the design a macro level prototype was formulated where a variable frequency inverter was used to drive an electromagnet to set up oscillations in the cantilever beam. The set-up is shown in Fig.10. 2 1 3 4 5 The Description of the Set Up is as follows: 1 : Cantilever Beam 2 : Variable Frequency Inverter 3 : Electromagnet to generate vibrations 4 : Copper Coils 5 : NdFeB Magnet
790 Ankita Kumar et al. / Procedia Computer Science 79 ( 2016 ) 785 792 Fig.10 Macro Level Prototype Design of Energy Harvester The number of coils are 20 for this set up. The voltage measurement for two lower frequencies i.e. 12.5 Hz and 50 Hz has been carried out. The results obtained over a DSO to measure the voltage generated by the prototype setup. Fig.11 Voltage Generated for 12.5 Hz of Frequency Fig.11 shows that the voltage generated for 12.5 Hz of frequency and 20 turns of Copper coil is 40 mv i.e. 2mV per turn. Fig.12 Voltage Generated for 50 Hz of Frequency Fig.12 shows that the voltage generated for 50 Hz of frequency and 20 turns of Copper coil is 20 mv i.e. 1mV per turn. This proves that the designed prototype for electromagnetic energy harvester works on the principle of electromagnetic induction. To maximize the voltage output generated MEMS technology is being used and instead of Copper, Aluminium is preferred because the etching rate of Aluminium is much higher than Copper in MEMS. Also, for higher voltage generation Aluminium is preferred. Since, increasing number of turns is not feasible is MEMS fabrication process so
Ankita Kumar et al. / Procedia Computer Science 79 ( 2016 ) 785 792 791 a series of cantilever beams with single turn will be fabricated to maximize the output. An array of 6 cantilever beams is thus being simulated for this purpose. 6. Electromagnetic Energy Harvester Fabrication The fabrication steps suggested for such type of energy harvester are given in Fig 13. These fabrication steps are compatible to CMOS technology and hence has future scope. Fig 13a shows the fabrication flow for the silicon cantilever beam with Aluminium coil on a wafer1. Fig 13b shows the fabrication flow for the NdFeB magnet to be installed on silicon anchor on wafer2. However, this energy harvester needs to be wafer bonded i.e. wafer-1 and wafer-2 needs to be bonded to obtain the complete system. Hence, last step will be wafer bonding as shown in Fig 14. 7. Results and Discussions In comparison with available studies on MEMS-based Electromagnetic Energy Harvesters, the design proposed and discussed here is a framework to obtain a simple device to detect frequency changes. [8] Such analysis was possible based on the electromagnetic induction principle and applying the same to MEMS. Accounting for the very low cost of commercial MEMS market if an effective methodology can be developed for this energy harvester, it can prove a great boon to the electronics market where the major area of concern still remains the power reduction and battery life. Also, the vibrations are used to produce voltage which can drive supporting circuitry as shown in Fig.1. Hence, a self-driven monitoring system can been designed [9]. (a) Fig 13 Fabrication Flow (b) Fig. 14 Wafer Bonding
792 Ankita Kumar et al. / Procedia Computer Science 79 ( 2016 ) 785 792 8. Conclusion MEMS based Electromagnetic energy harvester design is a promising field which utilizes the waste vibrations and converts it into useful energy. The results obtained prove that the harvester is effective at miniscule frequency of vibration [9]. 32.41% increase in generated voltage is obtained with modified electromagnetic induction based cantilever design at 100 Hz frequency. Furthermore, the wiring connections involved in current systems would be eliminated altogether, if such dynamically operated MEMS systems were to be used. This existing design of the energy harvester can be further modified for increased accuracy and to provide for self-powered mechanism. However, to maximize the voltage generated frequency of MEMS cantilever beam needs to be minimized, the research for which is being carried out. Also, the fabrication of the same will be carried out to verify with the results of the macro design. References 1. Matthew J. Whelan, Michael V. Gangone, Kerop D. Janoyan, Ratneshwar Jha; Real-Time Wireless Vibration Monitoring For Operational Modal Analysis of an Integral Abutment Highway Bridge, Elsevier. Engineering Structures 31(10), 2224-2235Online version available at: http://www.sciencedirect.com/science/article/pii/s0141029609001291 2. Ankita Kumar, S.S. Balpande, MEMS Based Bridge Health Monitoring System; International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009 Volume- 2, Issue-4, Oct.-2014. Online version available at: http://www.iraj.in/journal/journal_file/journal_pdf/6-87-141258684314-18 3. M. Ferraria, D. Alghisi, M. Baù, V. Ferrari; Nonlinear Multi-Frequency Converter Array for Vibration Energy Harvesting in Autonomous Sensors, Elsevier. Procedia Engineering Volume 47, 2012, Pages 410 413 Online version available at: http://www.sciencedirect.com/science/article/pii/s1877705812042348 4. Özge Zorlua*, Haluk Külaha; A Miniature and Non-Resonant Vibration-Based Energy Harvester Structure, Elsevier. Procedia Engineering Volume 47, 2012, 664 667 Online version available at: http://www.sciencedirect.com/science/article/pii/s1877 70581204297X 5. S. Roundy, P. K. Wright, A Piezoelectric Vibration Based Generator for Wireless Electronics, Elsevier. Smart Materials and Structures13 (2004) 1131-1142. Online version available at: http://iss.mech.utah.edu/files/2012/10/smartmatandstruct-roundy-2004 6. Timoshenko, S., (1953), History of strength of materials, McGraw-Hill New York 7. Huicong Liua, You Qianb, Chengkuo Leeb; A Multi-Frequency Vibration-Based MEMS Electromagnetic Energy Harvesting Device, Elsevier. Sensors and Actuators A 204 (2013) 37 43Online version available at: http://www.sciencedirect.com/science/article/pii/s0924424713004603 8. Ankita Kumar, S.S. Balpande; Energy Scavenging From Ambient Vibrations Using MEMS Device, International Journal of Scientific Progress And Research (IJSPR) ISSN: 2349 4689 Volume-05, Number -01, 2014 9. Salem Saadon, Othman Sidek; Shape Optimization of Cantilever-based MEMS Piezoelectric Energy Harvester for Low Frequency Applications, IEEE, Computer Modelling and Simulation (UKSim), 2013, Pages 202-208, ISBN: 978-1-4673-6421-8.Online version available at: http://ieeexplore.ieee.org/